Trace alpha-particle detection system for water networks: from direct detection in liquid phase to identification – ActiFind

The new approach is based on a conductive B-NCD diamond layer that is deposited by microwave assisted CVD on a silicon alpha radiation detector.

The operation of the device is performed in two distinct steps:
- The first step is the electro-precipitation of the ions of the actinides. For this purpose, the aqueous medium to be analyzed, supposedly containing actinides is chemically adjusted in both pH and salt concentration (Na2SO4 or NaNO3). The adjustment of the pH to a value in the range of 3 and 4.5 is necessary, as well as that of the basic complexing salt to a concentration of 0.3 M to allow the control of both the hydrolysis of actinide ions and their complexation. The charge of salt thus added provides good conductivity of the electrolyte reducing the voltage drop across the electrolytic cell. The electro precipitation of actinide ions on the surface of boron doped diamond (cathode) is made by connecting a negative bias to the sensor and the positive one to the anode here made from a platinum wire. The operating mode is the galvanostatic mode at low current densities (-1.5< J <- 6 mA/cm2) and vigorous stirring (103 rpm) for a period of 120 minutes. - The second step consists of the measurement the electro-precipitated actinide ions on the surface of the cathode composed by B-NCD diamond. A typical alpha spectrometry chain is used to probe the signal from the Si/B-NCD device. The alpha particles from the precipitated actinide layer on the diamond film will interact in the silicon ionization chamber inducing current pulses (Figure 1). The number of counts recorded by the detector is proportional to the amount of alpha species present at the diamond surface, and the signal amplitude to the alpha energy allowing actinides identification. As a result, it comes very accurate to probe the actinide concentration in the solution thanks to a prior calibration of the device.

Parametric study
An important aspect of the electroprecipitation process is the reaction kinetics. In the present case, kinetics data of electroprecipitation of actinides on B-NCD layers should be collected in order to know the minimum electrolysis time necessary for reaching a maximum deposition yield. Maximum deposition yields around 80 % are obtained in nitrate media in comparison to 60 % for the sulfate one. Deposition time of 90 minutes seems to be the minimum value to reach equilibrium for the electroprecipitation process. The minimum current densities and the optimized pH values for a maximum deposition yield of Am-241 are 1 mA/cm2 at pH 4 in a sulfate medium and 3 mA/cm2 at pH 3 for a nitrate medium.

Direct actinides spectrometry measurements
We give here two examples of direct alpha spectrometry in solution from mixtures of actinides (see figure 1). The poor resolution obtained is due to the use of type Si-PIN commercial detectors instead of the not yet available PIPS detectors from CANBERRA. We were however able to make a very correct experimental deconvolution thanks to the use of the COLEGRAM Software developed by the Henri Becquerel National Laboratory (CEA)

Short term
1) Study of the deposition of B-NCD onto PIPS detectors from CANBERRA
2) Use of larger area detectors to increase electro-precipitation of the actinides ions
Long term
1)Study of a a new way for immobilization of the actinides ions onto the alpha detector. Evaluation of the possibility of grafting chelating agents on the B-NCD surface for extraction of actinides ions.
2)Envisage the possibility of using a single-crystal diamond as a substitute for commercial PIPS detector

M. Pomorski, J. de Sanoit, C. Mer, Ph. Bergonzo.,
Actinides traces spectrometry in liquids using electrochemically assisted boron doped diamond/silicon sensors. Journal New Diamond Forum Vol 28, N° 1, (2012) 21-27

J. de Sanoit, M. Pomorski et P. Bergonzo.,
Projet ActiFind. Traces d’émetteurs alpha dans les réseaux publics. De la détection directe en phase liquide à l’identification. WIGSG 2012 – Workshop Interdisciplinaire sur la Sécurité Globale. 24-25 janvier 2012. Université de Technologie de Troyes, France

J. de Sanoit, T.Q. Tran, M. Pomorski, S. Pierre, Ch. Mer-Calfati, Ph. Bergonzo.,
Design of an electrochemically assisted radiation sensor for alpha-spectrometry of actinides traces in water. Applied Radiation and Isotopes. Vol 80 (2013) 32-41

Q.T. Tran, M. Pomorski, J. de Sanoit, C. Mer-Calfati, P. Bergonzo.,
Optimization of the efficiency of diamond based alpha-particles sensors for spectrometry of actinide trace in aqueous solutions.
I.E.E.E., Transactions on Nuclear Science, Vol x (2014) xx-xx (accepted for publication)

T. Q. Tran, M. Pomorski, J. de Sanoit, S. Pierre and P. Bergonzo.,
Electroprecipitation of actinides traces on diamond/Si PIN sensor for alpha -Spectrometry in aqueous solutions. Workshop Inter-disciplinaire sur la Sécurité Globale (Université de Technologie de Troyes 30 et 31 janvier 2014)

The quality of the water we use every day is an essential governing parameter of the public health. In our societies, the preservation of the integrity of the drinking water supply is considered as a major stake. Numerous pollutants can affect more or less durably the quality of the water which we use every day. Besides classic contaminants as organic products, heavy metals, and bacteriological pollutants, the quality of the water can be also severely affected by radioactivity. Vulnerability of drinking water distribution systems to deliberate attacks, which would have major public health, economic, and psychosocial consequences, is one of the main issues of concern to governmental agencies and water supply authorities. The water network can be seen as vulnerable to attacks created by nuclear accidents or by terrorist’s attacks such as contamination through reservoirs, back-flow from domestic water supply taps, etc. The recent example of Fukushima alerted the world on the weakness of our modern societies to a radioactive contamination of our supply chains for essential needs such as water, but also food, beverages etc. In the case of such an extremely alerting situation, the alpha activity is probed after the full evaporation of the liquid media of a selection of test samples. This process is slow, requires a lot of energy, and is “destructive” since the test sample cannot be used any further. Also, it does not work in complex systems like wastewater, drinks, urine, milk etc where the solid residue is preventing the measurement. In this project we propose to realize a novel sensor platform to probe the activity of trace levels of actinide contaminants in water. So far, no system exists that is enabling the measurement of radioactive water in a portable, easy to handle system that can be established for early stage detection of “nuclear attacks” as well as for permanent water quality monitoring. Here therefore the main objective of the project is the realization of a high sensitivity alpha-particle detection system working directly in liquid phase for the detection of dissolved actinides. According to the measurement duration, values in the Bq/l range are reachable. The main breakthrough is that the system enables real time monitoring, includes a water pre-cleaning fluidic system, can be cleaned using electrochemical decontamination, and will be portable thus requiring low energy, and easy to use. The work is based on and earlier development conducted by the CEA-LIST partner and validated on contaminated floor cleaning soiled waters. The patented approach will be here pre-industrially developed and adapted to a commercially available technology, combining sensor to electronics and readout system.
Also, the coupling of the system to an integrated microfluidic capillary electrophoresis platform will be developed in order to render the system compatible with more complex solutions than water. Based on the expertise of the project partners, ACTIFIND aims at developing a valid industrially available system that will be tested within the consortium on real environmental solutions, as well as more complex systems such as wastewaters and beverages. Further extension of the system will explore the possibility to use it as a decontaminating system on scaled up basis.